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Steel strength question

I am new to the welding hobby. I have had my MM 211 for a couple of weeks now, and just got through building some angle iron horses so I don't always have to work from the floor.

One of the main reasons I wanted my own welder was so I could build my garage furniture so I can actually create enough space to work comfortably in and occasionally park my truck in it.

I have drawn out plans for a shelf system that is 7' wide, 18" deep, and about 6' high. I am wanting to use 1.5 inch square tubing with a 14 gauge wall. The way I have designed it, I would build four shelves 7'x18" and separate them with 17.5" tubes. I would not have a bottom shelf, but cut some plate for the feet to stabilize it a little more. I will be using 3/4" plywood for the shelves attached with screws with welded on tabs.

My concern is how much weight it will hold before I start seeing bowing in the shelves, and if I should be bracing the shelves at the center point as well. I won't be putting massive items on the shelves, but I am curious to what it's limitations would be. I might be moving into a larger place and would carry the design over if this one works out.

I don't think there is enough information here to answer the question. Would this shelving unit legs in each corner, maybe two more in the center of the span? Or is going to have two legs with shelves cantilevered out and be bolted to the garage wall? The shorter the unsupported spans the stronger it will be.

It will hold quite a load....if you were to cut a 7' leanth and set each end on a block and stand (or add pressure) it will give you a pretty good idea. Remember you will have two supports, one in front and one if the rear (plus the plywood) so if one will hold your weight two will double the load. that should give you a good idea. Should atleast hold a roll of mig wire for the new mig and the miter saw.

The shelf unit you showed is similar to some we have at work. Three feet wide and 18" deep, with a stamped sheet metal shelf. I believe they are rated at 110 lbs. per shelf. One main difference is they have added diagonal cross bracing on the back and sides, they wobble pretty bad without them.With 1.5" square tubing welded together this probably won't be a problem. They should support a substantial load before showing any signs of stress, even with the 7' span. In the event they sag too bad with whatever you load on them, you could always go back and add a center support later right up the middle. You could add them up the back side between the shelves first. Then if that's not enough add another set on the front. But if you put enough weight on it to start making the shelves sag in the original configuration, it's going to be a chore to unload, reinforce and reload again. That will be ALOT of weight.You might also think of adding some tabs on the back to secure it to the wall studs with lag bolts to make sure it stays put. Or if it's going on a concrete floor maybe some on the bottom of the legs to anchor it to the slab or a combination of both.Good luck and let us see how it goes and turns out.

I would say that 200 pounds per shelf would be fine. Even with 200 pounds in the center you should have less than 1/2 inches of deflection. You shouldn't get permanent deflection until it sags an inch in the center.

Even with 800 pounds total, 4 shelves at 200 each, the legs will be well within the permissible load to avoid buckling. So if your welds are good enough the material is strong enough for this kind of loading.

I would say that 200 pounds per shelf would be fine. Even with 200 pounds in the center you should have less than 1/2 inches of deflection. You shouldn't get permanent deflection until it sags an inch in the center.

Even with 800 pounds total, 4 shelves at 200 each, the legs will be well within the permissible load to avoid buckling. So if your welds are good enough the material is strong enough for this kind of loading.

I agree although the deflection with a 200 pound point load distributed over two 84" spans would be much less than 1/2 inch with stress in the 10,000 PSI range. And with the plywood shelf, the load would be somewhat distributed. Uniformly distributed load of 200 pounds over two 84" spans would have a center deflection of 3/16" and stress in the 6000 pound range. Typical hot rolled square tube has a yield in the 34-38 ksi range.

The real issue here would be securing the shelf to the wall as it would be quite unstable. And the weld quality is a limiting, unknown variable. Sure, 14 gauge (0.075") is easily welded with GMAW but tee joints like to burn the branch and barely penetrate the run.